Interrelationship of micromechanics and morphology of fibroblasts adhered on different polymeric surfaces

Abstract

The membrane stiffness ( ε) of rat lung fibroblasts (RLFs) adhered on different polymeric surfaces was probed by atomic force microscopy. The corresponding cell morphology was also analyzed to probe its interrelationship with ε. Two tyrosine-derived polymer families, poly(DTR glutarate)s and poly(DTE-co-PEG 1000 carbonate)s with systematic variations in the chemical composition and physical properties, notably surface hydrophilicity, were used. The cell membrane of adhered RLFs was indented by a probe tip. ε was obtained by best-fitting the relationship of applied tip forces and the indentation depth with the Hertz model. Excluding tissue culture polystyrene, non-PEG-containing polymers are generally hydrophobic and the changes in chemical composition do not elicit significant changes in ε. In contrast, polymers containing as little as 2 mol.% PEG display a major increase in surface hydrophilicity and invoke a substantial decrease in ε. Additionally, RLFs show a high degree of spreading and fibroblastic appearance on non-PEG-containing polymers, but much less spreading and axial morphology when PEG is present. A mechanism is proposed to explain how a cell maintains its structural integrity on different polymeric surfaces: the degree of cell spreading is higher on non-PEG-containing surfaces than on PEG-containing ones, resulting in more extended cytoskeletal filaments and hence a stiffer cell membrane. Our studies shed light on the use of cellular micromechanics, and in particular membrane stiffness, to characterize cell response as a function of the chemical composition of the underlying substrata.